| From: | Michael Paquier <michael(dot)paquier(at)gmail(dot)com> |
|---|---|
| To: | Masahiko Sawada <sawada(dot)mshk(at)gmail(dot)com> |
| Cc: | Fujii Masao <masao(dot)fujii(at)gmail(dot)com>, Robert Haas <robertmhaas(at)gmail(dot)com>, Petr Jelinek <petr(at)2ndquadrant(dot)com>, Vik Fearing <vik(at)2ndquadrant(dot)fr>, Simon Riggs <simon(at)2ndquadrant(dot)com>, Josh Berkus <josh(at)agliodbs(dot)com>, PostgreSQL-development <pgsql-hackers(at)postgresql(dot)org> |
| Subject: | Re: Quorum commit for multiple synchronous replication. |
| Date: | 2016-12-06 10:14:31 |
| Message-ID: | CAB7nPqTYPzLFrp7=AESjK_Y--9K0UJq8+zR88OMvRR6rM0Ekog@mail.gmail.com |
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| Lists: | pgsql-hackers |
On Tue, Dec 6, 2016 at 6:57 PM, Masahiko Sawada <sawada(dot)mshk(at)gmail(dot)com> wrote:
> On Tue, Dec 6, 2016 at 1:11 PM, Fujii Masao <masao(dot)fujii(at)gmail(dot)com> wrote:
>> If M (i.e., number of quorum sync standbys) is enough large,
>> your choice would be good. But usually M seems not so large.
>>
>
> Thank you for the comment.
>
> One another possible idea is to use the partial selection sort[1],
> which takes O(MN) time. Since this is more efficient if N is small
> this would be better than qsort for this case. But I'm not sure that
> we can see such a difference by result of performance measurement.
>
> [1] https://en.wikipedia.org/wiki/Selection_algorithm#Partial_selection_sort
We'll begin to see a minimal performance impact when selecting a sync
standby across hundreds of them, which is less than say what 0.1% (or
less) of existing deployments are doing. The current approach taken
seems simple enough to be kept, and performance is not something to
worry much IMHO.
--
Michael
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